Currently, silver halide photographic materials are being developed to have a higher sensitivity and to have a more small-sized format, and photographic light-sensitive materials having far higher sensitivity and image-forming quality are strongly required.
Accordingly, the requirements for silver halide emulsions for photographical use have become even more sever, and the photographic characteristics of photographic materials are required to have an even higher level of an already high sensitivity, a high contrast, excellent graininess and sharpness, etc.
Methods of manufacturing tabular grains and techniques for the use of the grains are disclosed in U.S. Pat. Nos. 4,386,156, 4,504,570, 4,478,929, 4,414,304, 4,411,986, 4,400,463, 4,414,306, 4,439,520, 4,433,048, 4,434,226, 4,413,053, 4,459,353, 4,490,458 and 4,399,215, which are intended to attain the elevation of the sensitivity, including the elevation of the color sensitization efficiency by the use of sensitizing dyes, as well as the improvement of the relation of sensitivity/graininess, the improvement of the sharpness and the elevation of the covering power, for the purpose of satisfying the above-mentioned requirements.
Further, Japanese Patent Application (OPI) Nos. 113930/83, 113934/83 and 119350/84 (the term "OPI" as used herein means a "published unexamined Japanese patent application") illustrate multilayer color photographic materials which have an emulsion of tabular silver halide grains with an aspect ratio of 8/1 (also expressed, e.g., 8:1, or simply 8) or more in the high sensitive layer and which have an elevated high sensitivity and improved graininess, sharpness and color reproducability.
These patent publications mention that the incorporation of tabular grains into a blue-sensitive layer is effective for improving the sharpness of photographic materials, since the tabular grains are hardly scatterable, and the incorporation of the grains into a green-sensitive or red-sensitive layer is also effective for improving the graininess of the materials.
Japanese Patent Application (OPI) No. 77847/86 illustrates multilayer color photographic materials which have an emulsion of tabular silver halide grains with an aspect ratio of 5/1 or more in a high sensitive layer and a monodispersed silver halide emulsion in a low sensitive layer and which have improved sharpness and color reproducability.
Research Disclosure No. 25330 illustrates a technical means of adjusting the thickness of the tabular grains in a photographic material so that the reflection of the light for the layer above the tabular grain-containing layer is enhanced to elevate the sensitivity of the upper layer or the reflection of the light for the said layer is minimized so it does not detract from the sharpness of the upper layer.
U.S. Pat. Nos. 4,435,501 and 4,459,353 illustrate a technical means of improving the sensitivity of tabular grains having a specific shape, in which silver chloride guest grains are epitaxially deposited on an already limited surface part of the host tabular grains as projections.
The epitaxial deposition of silver halide guest grains on host grains is disclosed by Berry and Skillman in their "Surface Structure and Epitaxial Growth in Silver Bromide Crystals" in Journal of Applied Physics, Vol. 35, No. 7, pages 2165-2169 (July, 1964).
U.S. Pat. No. 3,804,629 illustrates a means of depositing silver chloride on silver halide grains after the physical ripening and desalting of the silver halide emulsion, but prior to the chemical ripening thereof so as to improve the stability of the silver halide emulsion to metal dusts. This patent mentions that the silver chloride forms small projections on the silver halide host grains by the deposition.
British Patent 2,038,792A illustrates a method of selectively depositing silver chloride on corner parts of tetradecahedral silver bromide grains.
U.S. Pat. Nos. 3,505,068, 4,094,684 and 4,142,900 illustrate a technical means of epitaxially depositing silver chloride on silver iodide host grains.
However, the grains in which silver chloride has been epitaxially deposited on the host grains as mentioned above (that is, the grains having projections on the surface thereof) are thermodynamically extremely unstable so that these would be deformed when kept at a high temperature for a long period of time and, as an inevitable consequence, result in the decrease of sensitivity and the increase of fog, and accordingly, these grains are unfavorable in view of the manufacture step of silver halide emulsions.
In multilayer photographic light-sensitive materials having two or more emulsion layers, one emulsion is influenced by the other layer(s). For example, upon coating emulsion layers, one layer is influenced by the diffusion of halide ions, etc. from the other layer(s) so that the grains having projections on the surface thereof would easily be deformed, and therefore, it is difficult for the multilayer materials to obtain the same characteristics as those of single layer photographic light-sensitive materials. In addition, the multilayer materials are noticeably influenced by the storing conditions, for example, storing temperature, storing humidity, storing time, etc., because of the transference of the dye(s), anti-foggant(s), etc. from one emulsion layer to other(s). Accordingly, because of the same reason as mentioned above, the use of grains with projections in multilayer photographic materials is problematic with respect to the storage stability of the photographic materials.
On these grounds, although the technique of a) improving the graininess, sharpness and color reproducibility of multilayer photographic light-sensitive materials by the incorporation of tabular grains thereinto, as mentioned above, and the technique of b) elevating the sensitivity of silver halide emulsions by the epitaxial deposition of silver chloride on tabular grains, also as mentioned above, are excellent only independently, the combination of techniques a) and b) is, in practice, problematic for multilayer photographic light-sensitive materials.
Further, the epitaxial deposition of silver chloride on silver halide grains is often accompanied by deterioration of graininess together with the elevation of the sensitivity of the resulting grains. This means that the technique of such epitaxial deposition is not always sufficient for sensitization of the silver halide grains in view of the evaluation of the relation of sensitivity/graininess of the resulting grains.
British Patent 1,027,146 illustrates a technical means of coating a silver chloride shell over a monodispersed cubic silver bromide core grain to give silver halide grains having both the spectral responsiveness of the silver bromide and the developability of the silver chloride.
U.S. Pat. No. 4,414,306 illustrates silver halide grains containing silver chloride in the circular range of tabular grains.
However, the grains, which have been coated with a silver chloride shell to such degree that these may have the developability of the silver chloride, are accompanied by deterioration of the graininess, and additionally the coated grains often cause deterioration of the adsorbability of dyes.